UPDATED: March 13, 2018  5:05 PM

AUSTIN, Texas (CBSDFW.COM/CNN/AP) – A series of deadly package bombs delivered to homes in Austin has shaken residents and cast suspicion on one of life’s common occurrences — getting a package delivered to your doorstep.

Three package bombs have exploded at homes in the Texas capital over 10 days — including two Monday — killing two people and injuring two others. Investigators say they believe the incidents are related, and residents have responded anxiously in the past day.

Austin police announced a $50,o0o reward for information leading to an arrest in this case on Tuesday, along with the $15,000 reward announced by Governor Greg Abbott on Monday.

Austin police have received 265 calls about suspicious packages, Chief Brian Manley said Tuesday afternoon, though police haven’t indicated any subsequent check revealing anything alarming.

Chief Manley said the U.S. Postal Service is helping with the investigation into those suspicious packages.

He said there are similarities that link the three bombing cases but he wouldn’t go into detail to maintain the integrity of the investigation.

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Austin Police Chief Brian Manley (CBS11)

“What caused this in these instances was a suspicious package that no one was suspecting or expecting,” Austin Mayor Steve Adler told CNN Tuesday. “I want everyone in my community, if they see something that’s suspicious — a package or otherwise — I want them to pick up the phone and call 911.”

Daniel Arriaga told CNN affiliate KXAN he called authorities after he found a package he wasn’t expecting for his daughter.

“I don’t want to give the package to my daughter and something happens, and I would regret it for the rest of my life,” he told the station.

Meantime,  leader of Austin’s black community says the families of two people killed by separate package bombs knew each other.

Nelson Linder is the longtime president of the NAACP chapter in Austin. He said Tuesday that the two victims are related to well-known members of the black community in Texas’ capital city.

Authorities say 17-year-old Draylen Mason was killed Monday by an explosive left on his doorstep. The teen died nearly two weeks after 39-year-old Anthony Stephan House was killed by a similar package.

Linder says he doesn’t believe in coincidences.

“From everything I’ve heard about Draylon, he was an outstanding young man who was going places with his life,” said Chief Manley.  “And it’s an absolute tragedy that he’s no longer with us.” 

Manley said Mason’s mother is in the hospital in stable condition.

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Austin residents are being told to be vigilant about unexpected or suspicious packages at their door after a series of package bombs killed two people and critically injured a woman. (Austin PD)

Here’s what we know so far

• The first blast happened March 2, killing Anthony Stephan House, a 39-year-old African-American man.

• A bombing early Monday killed a 17-year-old African-American male, whom CNN is not naming because authorities haven’t identified him yet. A woman was also hurt in that blast with injuries not considered life-threatening, police said.

• Both House and the slain teenager are relatives of prominent members of Austin’s African-American community, The Washington Post reported. House was the stepson of Freddie Dixon, a former pastor at a historic black church in Austin, the Post said. Dixon is friends with the grandfather of the teen who was killed Monday, according to the newspaper.

• Another explosion around noon Monday severely wounded a 75-year-old Hispanic woman. She was in critical condition Tuesday morning, Manley told KXAN, the CNN affiliate.

• Police have not decided if these are hate crimes but said that’s considered a possibility because the victims are African-American and Hispanic. Adler said it is still too early to know the motive.

• The residents found the packages outside their houses, but none was delivered by the US Postal Service or delivery services such as UPS or FedEx, police said.

• The explosions were not in the immediate vicinity of the ongoing South by Southwest festival, and authorities said the bombings don’t appear connected to that event.

The blasts

The packages were placed in front of the residents’ houses, said Manley, the police chief. They appeared to be “average-sized delivery boxes, not exceptionally large,” Manley said.

The first blast on March 2 that killed House was initially regarded as an isolated incident, police said.

Then Monday, a blast was reported at 6:44 a.m., killing the teenager and injuring a woman.

“One of the residents went out front, and there was a package on the front doorstep,” Manley said. “They brought that package inside the residence, and as they opened that package, both victims were in the kitchen, and the package exploded, causing the injuries that resulted in the young man’s death and the injuries to the adult female.”

Then another blast happened hours later Monday, sending police scrambling from one crime scene to the next.

The latter explosion occurred after the 75-year-old found a package on her porch. When she picked up the package, it detonated.

Bombs required ‘a level of skill’

Manley said it took “a level of skill” to construct the three bombs.

The maker or makers put ” these bombs together; they’re transporting them to their intended location; and then actually … detonating them,” Manley told KXAN on Tuesday. “So there’s a certain level of skill and sophistication that whoever is doing this has, and … we are hoping to use the evidence we have to track them down based on what we are seeing on all three scenes that seem to be consistent.”

What to do about suspicious packages

Texas Attorney General Ken Paxton warned all Texans to be cautious. “With three reported explosions in the Austin area, I want to urge all Texans to report any suspicious or unexpected packages arriving by mail to local law enforcement authorities. Call 911 immediately if you receive something suspicious,” he said on Twitter.

Manley gave similar advice: “If you’ve received a package that has been left on your doorstep or left in your yard or left on your driveway that you were not expecting or that was not from someone you know, then give us a call.”

Residents seemed to be listening. Some have changed their habits when it comes to handling packages.

Trey Mathis checked to see if there was an address label on one that arrived.

“I took a walking stick and from behind my door, I cautiously tumbled the box over to bring up the label, where I could verify it was addressed to me and from the expected shipper,” Mathis said. “I resolved to post the picture onto social media (Instagram, then to Twitter and Facebook) to alert the USPS, if possible.”

Local police as well as the FBI and the Bureau of Alcohol, Tobacco, Firearms and Explosives are working on the case. And Gov. Greg Abbott announced a $15,000 reward for information leading to the arrest of the person or persons involved in the package blasts.

“I want the public to be aware and to be cautious because again we have two cases that are very similar, that have both resulted in a loss of life,” Manley said.

(© Copyright 2018 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.)